Conventional rolling bearing apparatus are constituted of an inner ring having an inner ring raceway track on its outer periphery, an outer ring having an outer ring raceway track on its inner periphery, a plurality of rolling elements interposed between the inner ring raceway track and the outer ring raceway track in a freely rollable manner, and a cage disposed between the inner ring raceway track and the outer ring raceway track in a freely rotatable manner so as to guide and hold the rolling elements.
The lubrication of a rolling bearing apparatus is generally conducted by circulating a lubricating oil or grease or by enclosing a lubricating oil or grease in the bearing apparatus. However, when the bearing apparatus works, the lubricating oil or grease flies off or vaporizes to emit a gas, especially at high temperatures in a vacuum environment or the like, to thereby contaminate the atmosphere surrounding the bearing apparatus. Because of this, neither a lubricating oil nor a grease can be used in clean rooms or apparatuses requiring a clean atmosphere, such as apparatuses for producing semiconductors, liquid-crystal panels, hard disks, etc., or in a severe environment such as a high-temperature or vacuum atmosphere, a special atmosphere, a very-low-temperature atmosphere, or a radiation exposure atmosphere.
JP-A-55-57717 (the term "JP-A" as used herein means an "unexamined published Japanese patent application") and JP-A-61-55410 disclose a lubrication technique which comprises forming beforehand a thin lubricating film consisting of molybdenum disulfide, tungsten disulfide, graphite, silver, lead, gold, etc. by sputtering, ion plating, baking, thermal spraying, etc. on part or all of the inner ring, outer ring, cage, and rolling elements.
In JP-A-62-151539 and JP-A-64-79418 is disclosed a lubrication technique in which a cage made of an sintered alloy obtained from a mixture of a solid lubricant, e.g., molybdenum disulfide, tungsten disulfide, graphite, or hexagonal boron nitride, and a metal powder is used to allow a component of the cage to be released from the cage due to frictional contact between the cage and the rolling elements and deposit on the rolling elements, inner ring, and outer ring to form a thin lubricating film thereon.
Furthermore, JP-A-2-245514, JP-A-4-102718, and Japanese Patent 2,709,119 disclose a lubrication technique in which a cage made of a resin composition comprising a plastic, a solid lubricant, etc. is used to allow a component of the cage to be released from the cage due to frictional contact between the cage and the rolling elements and deposit on the rolling elements, inner ring, and outer ring to form a thin lubricating film thereon.
On the other hand, with the trend toward performance elevation, yield increase, etc. in devices and apparatuses, the conditions under which processes are conducted are becoming severer. Namely, the severe conditions such as higher temperatures, higher degrees of vacuum, etc. are required. With respect to the bearing apparatuses used therein, it is required to be reduced in the outward flying of particles therefrom and to work smoothly over long in severe environments, e.g., in a higher-temperature atmosphere or a higher degree of vacuum. These requirements are becoming higher year by year.
However, the lubrication technique due to a thin lubricating film formed previously, as disclosed in JP-A-55-57717, JP-A-61-55410, etc., generally has a short bearing life, because the lubricating film wears, as the bearing works, and finally disappears due to the frictional force in contact areas, resulting in no lubricating effect and hence in base metal (base material) adhesion/baking.
In the case where a cage is constituted of a sintered alloy, as disclosed in JP-A-62-151539 and JP-A-64-79418, this technique has a drawback that the cage is extremely expensive because a complicated shape cannot be formed and, hence, a desired cage shape must be formed from a rod or ring material or the like through mechanical processing. In addition, the use of a sintered alloy has the following drawbacks. Although sintered alloys are generally excellent in heat resistance, sintered alloys have low mechanical strength and are brittle. Accordingly since sintered alloys tend to occur surface cracks during mechanical processing, they have poor mechanical proccessability. For example, the processing rates for example, cutting speed and cut depth must be reduced. When a bearing apparatus employing such a sintered alloy cage works, crack may progressed from, e.g., the cracks generated during the processing. As a result, there are cases where the cage suffers abnormal wear, damage, or breakage to cause a large amount of particles to fly off the bearing apparatus or to make the bearing apparatus unable to work.
Furthermore, the prior art cage made of a resin composition as disclosed in JP-A-2-245514, JP-A-4-102718, Japanese Patent 2,709,119, etc. has a drawback that since the base resin material itself has insufficient lubricity, its lubricating effect is lost in an early stage after the bearing apparatus begins working. As a result, there are cases where the amount. of particles worn is rapidly increased and this causes a large amount of particles to fly off the bearing apparatus or causes the bearing to have a significantly increased torque and thus end its life. In addition, since this prior art cage has insufficient heat resistance due to the glass transition point and melting point of the resin material itself, the wear resistance and lubricity of the cage deteriorate considerably when the bearing apparatus works in a high-temperature environment. On the other hand, in the case where a tetrafluoroethylene resin having lubricity is employed as a base material, it is necessary to obtain a desired cage shape from a rod or ring material or the like through mechanical processing because the resin is not melt-moldable, as in the case of the sintered alloy described above. Hence, the cage thus produced is highly expensive.
As described above, conventional rolling bearing apparatuses have the following problems. Especially in a high-temperature environment, long-term lubrication is difficult and a large amount of particles fly off the bearing. Cages for use therein are extremely expensive because of the necessity of mechanical processing. Some materials for cages have poor mechanical proccessability, so that there are cases where trouble is generated when the bearing apparatuses are working.